For a frame of reference:
During the Sunset period I "tested" my i7's APU to see just how much it could do. Now I don't think I was getting Ultra (with everything else shut down), but I was getting good enough to play without really stressing it out. I managed to get something like 7 concurrent instances of the game running comfortably (at <10FPS :p) before I ran out of RAM.
Desktop (so it let me allocate sys RAM)
Win7 x64
16Gb DDR3
i7 3770k (something between 512Mb-1.5Gb allocated to the APU)
Since you have a more modern APU, then you should handle one instance just fine, but I'd turn off any non-essential apps from the tray.